VBOs and glDrawElements() with JOGL

OpenGL OpenGL: Advanced Coding
1

Hi

When I use VBOs with glDrawArrays() it works fine. However, when I use glDrawElements() instead I keep getting the following exception:

element vertex_buffer_object must be disabled to call this method

at the glDrawElements() call.

Does anyone have a solution to this highly confusing aspect of VBOs?

PS. I am using JOGL and don’t know if the problem arises due to the versions of glIndexPointer() and glDrawElements() called.

Thanks

Graham


        if (mIsUsingVertexIndices)
        {
            IndexTriMesh3D triMesh = (IndexTriMesh3D)mGeometricObject;
            int numberTriangles = triMesh.numberTriangles();
            int numberIndices = 3 * numberTriangles;
            
            glv.glEnableClientState(GL2.GL_VERTEX_ARRAY);           // enable vertex arrays
            glv.glEnableClientState(GL2.GL_ELEMENT_ARRAY_BUFFER);   // enable vertex indices
            glv.glEnableClientState(GL2.GL_COLOR_ARRAY);            // enable colour arrays

            glv.glBindBuffer(GL2.GL_ARRAY_BUFFER,mVBO);
            glv.glVertexPointer(3, GL.GL_FLOAT, 0, 0);              // set the vertex pointer
                       
            glv.glBindBuffer(GL2.GL_ARRAY_BUFFER,mVBOColours);
            glv.glColorPointer(3, GL.GL_FLOAT, 0, 0);
            
            glv.glIndexPointer(GL2.GL_UNSIGNED_INT, 0, mVertexIndices);
            glv.glDrawElements(GL2.GL_TRIANGLES, numberIndices, GL.GL_UNSIGNED_INT, mVertexIndices); 
            
            glv.glDisableClientState(GL2.GL_VERTEX_ARRAY);          // disable vertex arrays
            glv.glDisableClientState(GL2.GL_ELEMENT_ARRAY_BUFFER);  // disable vertex colour array
            glv.glDisableClientState(GL2.GL_COLOR_ARRAY);           // disable vertex colour array
        }
2

http://www.opengl.org/wiki/Common_Mistakes:_Deprecated

Also
glEnableClientState(GL2.GL_ELEMENT_ARRAY_BUFFER)
doesn’t make any sense.

You can also look at
http://www.opengl.org/wiki/VBO_-_just_examples

and also
http://www.opengl.org/wiki/Vertex_Buffer_Object
http://www.opengl.org/wiki/VBO_-_more

3

Hi

Thanks for your reply and the links. I’ve now got it working. The error was in allocating the size of the indices buffer.

My working code block is now:


        if (mIsUsingVertexIndices)
        {
          IndexTriMesh3D triMesh = (IndexTriMesh3D)mGeometricObject;
          int numberTriangles = triMesh.numberTriangles();
          int numberIndices = 3 * numberTriangles;
          
          glv.glEnableClientState(GL2.GL_VERTEX_ARRAY);           // enable vertex arrays
          glv.glEnableClientState(GL2.GL_COLOR_ARRAY);            // enable colour arrays
    
          glv.glBindBuffer(GL2.GL_ARRAY_BUFFER,mVBO);
          glv.glVertexPointer(3, GL.GL_FLOAT, 0, 0);              // set the vertex pointer
                     
          glv.glBindBuffer(GL2.GL_ARRAY_BUFFER,mVBOColours);
          glv.glColorPointer(3, GL.GL_FLOAT, 0, 0);
          
          glv.glBindBuffer(GL2.GL_ELEMENT_ARRAY_BUFFER, mVBOIndices);
          glv.glDrawElements(GL2.GL_TRIANGLES, numberIndices, GL.GL_UNSIGNED_INT, 0); // note: the total number of indices
          
          glv.glDisableClientState(GL2.GL_VERTEX_ARRAY);          // disable vertex arrays
          glv.glDisableClientState(GL2.GL_COLOR_ARRAY);           // disable vertex colour array
        }